In recent years, improvement in handling the jumbo packets is demanded to address increase in the speed of communication devices and increase in the data amount transmitted and received in a network. Use of the jumbo packet is advantageous in that large volume of data can be processed in one packet. However, a prolonged processing of the jumbo packet may cause a delay in processing of other packets. Thus, when realizing co-existence of a service desired to possess real time property such as an Internet Protocol (IP) telephone and a service handling the jumbo packet in the same network, the jumbo packet is fragmented. The jumbo packet is fragmented when the size of a packet transferable to a destination network of the jumbo packet is smaller than the size of the jumbo packet. By fragmenting, multiple fragment packets are generated from one jumbo packet. Then, the generated multiple fragment packets are transmitted to the destination separately. A destination device restores the transmitted jumbo packet from the received multiple fragment packets. Thereafter, the destination device performs processing by using the restored jumbo packet.
As a related art, a mechanism is disclosed that records a data unit as a transmission target when performing transmission processing of one fragment generated from the data unit. The mechanism includes a queue for arranging fragments for transmission. When the queue exceeds a transmission capacity, the mechanism removes a data unit not recorded as the transmission target. As a related art, for example, Japanese Laid-open Patent Publication No. 11-177627 is disclosed. Also, a method is disclosed that fragments a packet including an Internet Key Exchange (IKE) payload exceeding a predetermined Maximum Transmission Unit (MTU) into packets smaller than the MTU. As a related art, for example, Japanese Laid-open Patent Publication No. 2003-244233 is disclosed.
It is assumed that a router, which has received a transmission packet transmitted from a transmission source device, fragments the transmission packet and transmits fragment packets to the destination. In this case, since the fragment packets are transmitted separately, some of the fragment packets generated from one transmission packet may be lost while being transferred. If any fragmented packet is lost while being transferred, the transmission packet might not be restored even if the other fragment packets reach the destination. Consequently, a device, which has received the fragment packets, determines that reception of the transmission packet has failed and discards the received fragment packets. That is, when one of fragmented packets is lost, the other fragment packets generated from the same transmission packet are not used. Thus, if the unused fragment packets are transmitted to the destination, communication efficiency between devices transmitting or receiving these fragment packets deteriorates.
Any of the disclosures described in documents cited as related arts is not effective in suppressing the deterioration of communication efficiency resulting from transfer processing of fragment packets not used due to missing of some of the fragment packets.